The use of plasmas for etching and other purposes is well known. A convenient reference paper on plasma etching is the paper by Paul J. Marcoux entitled "Dry etching--an overview", published in Hewlett Packard Journal, Aug. 1982, pages 19 to 23.
The equipment that is used to produce a plasma consists of:
(a) an electrically isolated chamber, usually called a discharge tube (within which the plasma is generated); PA0 (b) a vacuum pump (for creating and maintaining a low pressure in the discharge tube); PA0 (c) a supply of gas (for flushing air from the discharge tube and to provide a source of the ions and electrons which form the plasma); PA0 (d) a radio-frequency oscillator, amplifier and coupling network (as a source of power to establish the plasma); and PA0 (e) an antenna for coupling the rf power from the output of the coupling network into the plasma. PA0 (a) an electrically isolated, elongate, tubular cavity of uniform circular cross-section of diameter D, containing a gaseous source of ions and electrons at a pressure p; PA0 (b) first magnetic field-establishing means, external to the cavity, for establishing a magnetic field B within the cavity; PA0 (c) a radio-frequency antenna of length L, adapted to couple rf power into the gas within the cavity; and PA0 (d) a source of rf power of frequency f, external to the cavity, coupled to the antenna; the apparatus being characterised in that it includes PA0 (e) an electrically isolated auxiliary region connected to the cavity and at the same internal pressure as the cavity; and PA0 (f) second magnetic field-establishing means for establishing a required magnetic field configuration within the auxiliary region. PA0 (a) establishing a plasma in an electrically isolated, elongate, tubular cavity of uniform circular cross-section of diameter D, containing a gaseous source of ions and electrons at a pressure p, by establishing a magnetic field B within the cavity and coupling rf power of frequency f into the gaseous source using a radio-frequency antenna of length L located external to the cavity; and PA0 (b) allowing the plasma to extend into an auxiliary region having the same internal pressure p as the cavity and connected to the cavity.
Normally, the plasma tube is a metal cylinder of circular cross-section. However, cylinders of pyrex and quartz glass have been used by the present inventor (see the publications referred to below, in this paragraph). Among the antennas used to couple the rf power into the plasma, the most effective is a double loop antenna, which fits tightly against the sides of the discharge tube (see, for example, the experimental equipment described in the papers by (a) R. W. Boswell, in Physics Letters, Volume 33A, December 1970, pages 457 and 458, (b) R. W. Boswell et al in Physics Letters, Volume 91A, September 1982, pages 163 to 166, and (c) R. W. Boswell in Plasma Physics and Controlled Fusion, Volume 26, pages 1147 to 1162, 1984).